Petrol expenses.

I drive for a living, and am self employed. Since I fill out my own tax returns, and have to claim housing benefit and council tax support due to my low income, I am wondering what the best way to keep petrol receipts is?

My petrol receipts fade (get my petrol from Tesco and the receipts tend to fade, and sometimes, are barely visible) and I'm wondering what is acceptable proof of petrol expenses.

I tend to withdraw a set amount in cash every week/fortnight from my bank account to cover all of my expenses, including expenses unrelated to my work, including shopping/bills etc. I do this to make sure I stay within a strict budget.

Any advice? A friend who is also self employed says she doesn't keep petrol receipts, but instead writes down the exact amount of petrol she uses, and submits that, but housing benefit want to scan every petrol receipt I have.